The present invention relates to an apparatus for recording/reproducing a digital video signal or a digital audio signal on/from a magnetic tape, and more particularly, to an apparatus for controlling the relative position between a magnetic tape and a magnetic head during postrecording or dubbing operation.
FIG. 8 is an example of a schematic representation of a recording pattern produced by a magnetic recording/reproducing apparatus having a plurality of rotary magnetic heads. In this example, one frame of a television signal is divided across ten tracks. The digital video signal and the digital audio signal are recorded on the respective tracks in a time divisional manner (the structure of each track will be described in greater detail with reference to FIG. 9). Four channels of the digital audio signal can be recorded in a frame of a television signal. Two channels are recorded on the first five tracks of the frame, and the remaining two channels are recorded on the last five tracks of the frame.
Normally, this recording pattern is formed by one pair of magnetic heads whose azimuth angles are different from each other, and which are positioned at the opposite ends of a diameter of a circle (i.e., 180.degree. apart) formed by the outer periphery of a rotary drum. However, when digital signals are sequentially postrecorded or dubbed onto a track, a portion of a preceding track is overwritten in such a manner that its track pitch becomes smaller than the width of the magnetic head.
FIG. 9 is a schematic representation of a track in FIG. 8. The left end of the track lies at the head inlet (rush in) side, and the right side of the track lies at the head exit (separating) side. Each track is composed of an ITI (insert and track information) area, an audio data recording area, a video data recording area and a sub-code data recording area. The contents of these data recording areas are rewritable by way of dubbing.
No data is recorded on an overwrite margin area provided at the right end of the track, and on an IBG (interblock gap) area provided between the respective data recording areas. A pulse signal having the same frequency as the bit frequency of the data is recorded in the amble area, i.e., run up and guard areas, and the amble area is utilized as a PLL lock for extracting a bit clock during the reproducing operation. It should be noted that the overwrite margin provided at the right end portion of the track corresponds to a jitter margin.
FIG. 10 is an example of a schematic representation of the recording pattern corresponding to a two-channel digital audio signal. The digital audio signals in the first five tracks of a frame are assumed to be overwritten by the dubbing process. As illustrated in FIG. 10, the audio undercoat of track 9 (i.e., the previously recorded audio data which is being overwritten by dubbing) is magnetically reduced by the overwrite recording of track 0 and the audio undercoat of track 5 is magnetically reduced by the overwrite recording of track 4. Consequently, during the reproduction of tracks 5 and 9, the C/N (carrier to noise) ratio deteriorates and lowers the reproduction quality of the digital audio signals.